1. Field of the Invention
The present invention relates to a plasma display, and more particularly to the structure and drive of an AC memory type plasma display.
2. Description of the Related Art
A DC plasma display and an AC (AC memory type) plasma display are known conventionally. In particular, an AC memory type plasma display is widely used as a color display.
FIG. 9 illustrates the structure of a conventional AC memory type plasma display panel in cross section. As illustrated, this type of plasma display panel has a front substrate 41 and a rear substrate 45 which face each other and which are made of insulating material such as glass.
A plurality of transparent scanning electrodes 42a and maintaining electrodes 42b, formed from an ITO (Indium Tin Oxide) or Nesa film, are provided on the front substrate 41. Each of the scanning electrodes 42a and its corresponding one of the maintaining electrodes 42b form a surface discharge electrode 42. In order to reduce the resistances of the scanning and maintaining electrodes 42a and 42b, trace electrodes 43 are formed one on each of them. Normally, Cr/Cu/Cr (chrome/copper/chrome) stacked thin film electrodes or Ag (silver) thick film electrodes are employed as the trace electrodes 43.
A dielectric layer 44 is formed on the scanning electrodes 42a, the maintaining electrodes 42b and the trace electrodes 43. In general, lead glass having a low melting point is used to form the dielectric layer 44. An MgO film (not shown), having a thickness of approximately 0.5 xcexcm to 1 xcexcm, is formed on the dielectric layer 44 by vacuum vapor deposition, in order to prevent the dielectric layer 44 from being damaged by minus and plus ions and electrons, which are generated due to a gas discharge, and in order to lower a discharge voltage.
A plurality of data electrodes 46, which face the scanning and maintaining electrodes 42a and 42b and which are substantially perpendicular to the scanning and maintaining electrodes 42a and 42b, are formed on the rear substrate 45. Ag thick film electrodes are employed as the data electrodes 46. A white dielectric layer 47 is formed on the data electrodes 46. The white dielectric layer 47 is formed by printing and sintering glass paste prepared by mixing powder of white oxide (alumina, titanium oxide or the like), powder of lead glass having a low melting point, etc. The white dielectric layer 47 has the function of reflecting light emitted from phosphor layers 48 and directing the light toward the front substrate 41.
The phosphor layers 48 are formed on the white dielectric layer 47. The phosphor layers 48 are separate coatings of three phosphor materials applied onto the white dielectric layer 47 by thick film printing techniques and which respectively emit red, green and blue visible light when they are excited by ultraviolet rays generated due to the gas discharge.
The front and rear substrates 41 and 45 are arranged facing each other with a gap of 100 xcexcm to 200 xcexcm in between and with partition walls (not shown) in a lattice or stripe pattern being provided therebetween. The partition walls are made of a mixture of lead glass and one of magnesia oxide, titanium oxide, etc. A discharge gas, which essentially consists of a mixture of rare gases such as He (helium), Ne (neon) and Xe (xenon) gases, is filled in the gap between the front and rear substrates 41 and 45, and the peripheral portions of those substrates are sealed by a seal member. Employing the above-described structure, discharge cells 49 are formed between the front and rear substrates 41 and 45.
A drive method for the plasma display panel illustrated in FIG. 9 will now be described. This type of plasma display panel is driven by a subfield drive method such as that shown in FIG. 10. According to this drive method, a field which constitutes a single image is repeated about 50 to 70 times per second. Due to the afterimage effect, each field image displayed successively stays in the viewer""s eyes, which ensures a flicker-free natural image displayed on the plasma display panel.
A field is divided into a plurality of subfields. The subfields differ from each other in the number of maintaining pulses (the number of discharge times) generated during a maintaining period which will be described later. A multi-gradation image is displayed by combining the subfields into one field. For example, in the case of displaying a 64-gradation image, a field (F) is divided into 6 subfields (SF1 to SF6) as illustrated in FIG. 10. In each of the subfields SF1 to SF6, a preliminary lighting period, a preliminary erasing period and a writing period come in sequence, and a maintaining period follows. During the maintaining period, a surface discharge is caused between the scanning and maintaining electrodes 42a and 42b. The number of times the surface discharge is caused in the subfield SF1 is 32n (n: a positive integer). This number is progressively reduced by xc2xd at a time in the sequence of the subfield SF2 to the subfield SF6, whereby each subfield is weighted.
The drive operation of the above-described plasma display panel during one subfield period, more specifically, the discharge operation of a discharge cell 19, will now be explained with reference to FIGS. 11A to 11D illustrating the waveforms of drive voltage pulses. In FIGS. 11A to 11D, reference character D represents a train of data pulses to be applied to the data electrodes 46. Reference symbol SO denotes a train of drive voltage pulses to be applied to the 0th scanning electrode 42a. Reference symbol Sm represents a train of drive voltage pulses to be applied to the mth scanning electrode 42a. Reference character C denotes a train of drive voltage pulses to be applied to the maintaining electrodes 42b. 
In the preliminary lighting period which comes first, a preliminary discharge pulse PP is applied to all scanning electrodes 42a in order to cause a surface discharge between the electrodes 42a and 42b. In the next preliminary erasing period, pulses PE1, PE2 and PE3 are sequentially applied to the scanning and maintaining electrodes 42a and 42b in order to erase wall charges which have been generated between the electrodes 42a and 42b during the preliminary lighting period.
In the writing period, a writing pulse PW is applied to the selected scanning electrodes 42a of the plasma display panel so as to sequentially scan them. In synchronization with this, data pulses PD according to the display data are applied to the data electrodes 46. By so doing, a discharge between the selected scanning electrodes 42a and the data electrodes 46 supplied with the predetermined data pulses PD is caused at the opposite surfaces of those electrodes 42a and 46 such that wall charges are generated in the pixels supplied with the predetermined data pulses PD. In the next maintaining period, maintaining pulses PSUS are applied to the scanning electrodes 42a and the maintaining electrodes 42b so as to be superimposed on the wall charges. By thus superimposing the maintaining pulses PSUS, the discharge caused during the writing period is maintained as a surface discharge between the scanning and maintaining electrodes 42a and 42b. 
As explained above, according to the conventional AC memory type plasma display panel, the discharge caused between the opposite surfaces of the scanning and data electrodes 42a and 46 is utilized to write the display data in each pixel. The scanning electrodes 42a are covered with a magnesia oxide film which has excellent properties as discharge proof material, while the data electrodes 46 are covered with the phosphor layers 48.
Owing to the above structure, the potential of the scanning electrodes 42a is lower than that of the data electrodes 46 at the time of writing display data, as shown also in FIGS, 11B to 11D. This prevents positively charged particles, having a relatively large mass and whose sputtering efficiency is high, from impinging against the phosphor layers 48, and therefore prevents the phosphor layers 48 from being deteriorated or suffering damage due to the impingement. Furthermore, the luminance degradation and any variation in the discharge voltage, which would occur if the phosphor layers 48 were sputtered and the adhesion of material scattered therefrom were to occur, can also be prevented.
However, according to the conventional AC memory type plasma display panel described above, a weak discharge can occur between the scanning and data electrodes 42a and 46 at the timing the data electrodes 46 become lower in potential than the scanning electrodes 42a. The weak discharge, if occurs, may cause the impingement of the positively charged particles against the phosphor layers 48. Even if the potential at the scanning electrodes 42a is set lower than the potential at the data electrodes 46 prior to the writing of the display data, the impingement of electrons against the phosphor layers 48 can occur so as to impart any damage on the phosphor layers 48.
Because of the above, when still images such as characters are constantly displayed in fixed positions on the plasma display panel, those pixels of the phosphor layers 48 which are constantly in an ON state or which have a higher luminance become deteriorated faster than the other pixels. The deterioration of such pixels of the phosphor layers 48 results in the conventional AC memory type plasma display panel having a drawback of the occurrence of what is called a burning phenomenon, in other words, non-uniformity of luminance of the pixels.
Moreover, the speed of deterioration of the phosphor layers due to the impingement of the electrons or other charged particles differs depending on a difference in phosphor material between the phosphor layers for red, blue and green. This results in the conventional AC memory type plasma display panel having a drawback in that the range of phosphor material selection, when forming separate coatings of multi-color phosphor materials as the phosphor layers 48, is narrow.
Furthermore, since the opaque trace electrodes 43 are formed on the scanning electrodes 42a and the maintaining electrodes 42b, the aperture ratio of the pixels is small. Because of this, the conventional AC memory type plasma display panel has a further drawback in that the efficiency of use of the light emitted from the phosphor layers 48 is accordingly low.
Published Unexamined Japanese Patent Application (Kokai) No. 3-283233 discloses a DC plasma display panel of another type which has a feature in the structure of its electrodes. However, the electrodes of this plasma display panel is complicated in structure, and therefore cannot be applied to a color plasma display panel which requires the formation of the phosphor layers.
Published Unexamined Japanese Patent Application (Kokai) No. 7-182978 also discloses a DC plasma display panel in which the front substrate is provided with cathodes, while the rear substrate is provided with anodes perpendicular to the cathodes. In order to display images, a discharge is caused at the intersections of the cathodes and anodes. In this plasma display panel, however, the structure of a discharge space is complicated, and the phosphor layers need to be formed on a discharge path in order to realize color display. In this case, the impingement of the positively charged particles and the electrons, which would cause the deterioration of the phosphor layers, is unavoidable.
Published Unexamined Japanese Patent Application (Kokai) No. 5-101782 discloses a plasma display panel in which the surface discharge electrodes are provided on the partition walls of the rear substrate, while the phosphor layers are formed on both the front and rear substrates. In this plasma display panel, however, the data electrodes are arranged under the phosphor layers of the front substrate, and a discharge prior to driving causes the deterioration of the phosphor layers, as described previously.
In addition, Published Unexamined Japanese Patent Applications (Kokai) Nos. 6-318052 and 7-319423 disclose techniques for plasma displays. Those plasma displays have the structure wherein the electrodes provided on two substrates face each other, under which condition electrons and charged particles impinge on the phosphor layer when a discharge is caused between the electrodes.
It is accordingly an object of the present invention to provide a plasma display, which can suppress the deterioration of the phosphor layers due to the impingement of the charged particles and the electrons, and a drive method for the plasma display.
It is another object of the present invention to provide a plasma display, which can perform a writing discharge without any influence of a difference in phosphor material between the phosphor layers, and a drive method for the plasma display.
It is a further object of the present invention is to provide a plasma display, whose pixels have a large aperture ratio and which can utilize the light emitted from the phosphor layers with high efficiency, and a drive method for the plasma display.
It is a still further object of the present invention is to provide a plasma display, which can reliably perform a discharge at a low voltage, and a drive method for the plasma display.
It is a still further object of the present invention to provide a plasma display from which an internal impure gas can be efficiently removed.
It is another object of the present invention to provide a plasma display, whose drivers are fewer than conventionally used, and a drive method for the plasma display.
According to the first aspect of the present invention having the above-described objects, there is provided a plasma display comprising:
a first substrate on which are sequentially formed a matrix of surface discharge electrodes arranged in rows and columns, a plurality of scanning trace electrodes, a plurality of maintaining trace electrodes and a first dielectric layer, each of the surface discharge electrodes comprising a scanning electrode and a maintaining electrode arranged with a predetermined gap in between and which cause a discharge upon a voltage application, each of the scanning trace electrodes connecting the scanning electrodes included in one of the rows of the matrix, the maintaining trace electrodes intersecting the scanning trace electrodes with insulators being provided between the scanning trace and maintaining trace electrodes, each of the maintaining trace electrodes connecting the maintaining electrodes included in one of the columns of the matrix, and the first dielectric layer having an insulation property and covering the scanning electrodes and maintaining electrodes of the surface discharge electrodes, the scanning trace electrodes and the maintaining trace electrodes;
a second substrate facing the first substrate and on which are sequentially formed a second dielectric layer having an insulation property and a plurality of phosphor layers, the phosphor layers emitting predetermined visible light when they are excited by light generated due to the discharge caused between the scanning and maintaining electrodes; and
a discharge gas filled between the first and second substrates and which generates light due to the discharge caused between the scanning and maintaining electrodes.
In the above-described plasma display apparatus, the electrodes are not formed under the phosphor layers provided above the second substrate. Hence, a discharge through the phosphor layers does not occur, and therefore the phosphor layers are not deteriorated or damaged due to the impingement of the electrons and other charged particles, ensuring long life of the phosphor layers.
In the above-described plasma display, the first substrate may further be provided with first partition walls extending in a direction which is substantially perpendicular to the scanning trace electrodes, and having an insulation property to insulate the columns of surface discharge electrodes from each other and to define a discharge space between the first and second substrates. In this case, the maintaining trace electrodes can be arranged on the first insulating partition walls.
It is preferred that the scanning electrodes and the maintaining electrodes be narrower than a space defined between the first partition walls.
In the above-described plasma display, the second substrate may be further provided with second partition walls to define a discharge space between the first and second substrates. In this case, the phosphor layers can be arranged between the second partition walls.
In the above-described plasma display, the first substrate may be further provided with first partition walls extending in a direction which is substantially perpendicular to the scanning trace electrodes, and having an insulation property to insulate the columns of surface discharge electrodes from each other and to define a discharge space between the first and second substrates. Further, the second substrate may be further provided with second partition walls to define a discharge space between the first and second substrates. In this case, the maintaining trace electrodes can be arranged on the first partition walls, and while the phosphor layers can be arranged between the second partition walls.
Moreover, in this case, the second partition walls may be formed on the second substrate so as to intersect the first partition walls at right angles, and the first and second substrates may be arranged facing each other in a state in which the first and second partition walls are in contact with each other, with the discharge space being defined between the first and second substrates.
By so doing, in the above-described plasma display, an evacuation path to remove an impure gas from the plasma display is formed extending in vertical and horizontal two directions, and the evacuation conductance is improved accordingly. Therefore, the impure gas within the plasma display can be assuredly removed.
In the above-described plasma display, the first substrate may have a discharge proof thin film formed on the first dielectric layer and which is high in a count of discharged secondary electrons.
It is preferred that this thin film be made of magnesia oxide.
Such a thin film made of magnesia oxide or the like, formed on the first substrate, ensures a discharge between the scanning and maintaining electrodes, and permits a low voltage to be used to cause the discharge.
In the above-described plasma display, the scanning electrodes and the maintaining electrodes may be made of transparent electrode material, the scanning trace electrodes and the maintaining trace electrodes may be made of opaque metal material, and the first dielectric layer may be made of transparent insulating material.
In general, opaque metal electrodes having a sheet resistance lower than that of transparent electrodes are adopted as the scanning trace electrodes and the maintaining trace electrodes. In the above-described plasma display, however, since such opaque maintaining trace electrodes need not be formed on the maintaining electrodes, the aperture ratio of the pixels is improved, and the efficiency of use of the visible light emitted from the phosphor layers is improved accordingly.
In the above-described plasma display, it is preferred that the second dielectric layer has a property of reflecting predetermined visible light which the phosphor layers emit.
By virtue of using a material, having a property of reflecting the visible light emitted from the phosphor layers, as the second dielectric layer, the efficiency of use of the visible light emitted from the phosphor layers is further improved.
In the above-described plasma display, each of the phosphor layers may comprise one of three phosphor materials which are arranged in a predetermined order and which respectively emit red, green and blue light when they are excited by the light generated due to the discharge.
Generally speaking, the speed of deterioration due to the impingement of electrons or other charged particles differs depending on a difference in phosphor material between the phosphor layers. In the above-described plasma display, however, since the electrons or other charged particles do not impinge against the phosphor layers, a difference in the speed of deterioration due to the impingement does not occur. Therefore, the phosphor materials for red, green and blue, which are to be separately coated to provide the phosphor layers for use in a color display, can be chosen from a wide range of selection.
In the above-described plasma display, the electrodes are not formed under the phosphor layers. Therefore, a discharge between the electrodes is not influenced by a difference in phosphor material between the phosphor layers.
In this case, it is preferred that the second dielectric layer have a property of reflecting any visible light emitted from the phosphor layers.
In the above-described plasma display, the discharge gas may essentially consist of a rare gas mixture containing helium, neon and xenon, for example, and may emit ultraviolet rays for exciting the phosphor layers, due to the discharge caused between the scanning and maintaining electrodes.
According to the second aspect of the present invention, there is provided a plasma display comprising:
a plasma display panel which includes
a first substrate on which are sequentially formed a matrix of surface discharge electrodes arranged in rows and columns, a plurality of scanning trace electrodes, a plurality of maintaining trace electrodes and a first dielectric layer, each of the surface discharge electrodes comprising a scanning electrode and a maintaining electrode arranged with a predetermined gap in between and which cause a discharge upon a voltage application, each of the scanning trace electrodes connecting the scanning electrodes included in one of the rows of the matrix, the maintaining trace electrodes extending in a direction which is substantially perpendicular to the scanning trace electrodes and intersecting the scanning trace electrodes with insulators being provided between the scanning trace and maintaining trace electrodes, each of the maintaining trace electrodes connecting the maintaining electrodes included in one of the columns of the matrix, the first dielectric layer having an insulation property and covering the scanning electrodes and maintaining electrodes of the surface discharge electrodes, the scanning trace electrodes and the maintaining trace electrodes,
a second substrate facing the first substrate and on which are sequentially formed a second dielectric layer having an insulation property and a plurality of phosphor layers which emit predetermined visible light when they are excited by light generated due to the discharge caused between the scanning and maintaining electrodes, and
a discharge gas filled between the first and second substrates and which generates light due to the discharge caused between the scanning and maintaining electrodes;
a first driver connected to the scanning trace electrodes and which applies a voltage for selecting the scanning electrodes row by row and a voltage for causing, in interaction with a voltage applied to the scanning electrodes, a discharge between those of the scanning and maintaining electrodes where wall charges have been generated;
a second driver connected to the maintaining trace electrodes, and which applies a voltage according to display data to the maintaining electrodes corresponding to the scanning electrodes of a row currently selected by the first driver, and which applies a voltage for causing a discharge between those of the scanning and maintaining electrodes where wall charges have been generated depending on the voltage according to the display data; and
a controller which controls operations of the first and second drivers.
In the plasma display described above, only two types of electrodes, i.e., the scanning electrodes and the maintaining electrodes, are provided in the plasma display panel. Hence, only two drivers, i.e., the first and second drivers, will suffice to drive the plasma display.
In the above-described plasma display, the first driver may apply a first predetermined voltage for causing a discharge between each of the scanning electrodes and a corresponding one of the maintaining electrodes in order to generate wall charges therebetween. The first driver may apply a predetermined second voltage to the scanning electrodes, while the second driver may apply a predetermined third voltage to the maintaining electrodes, in order that the wall charges, generated between the scanning and maintaining electrodes, will be erased by an interaction between the predetermined second and third voltages. The first driver may apply a predetermined fourth voltage for selecting the scanning electrodes row by row, while the second driver may apply a predetermined fifth voltage according to display data to the maintaining electrodes corresponding to the scanning electrodes of a row currently selected by the first driver, in order that a discharge will be caused between the selected scanning electrodes and their corresponding maintaining electrodes so as to generate wall charges therebetween, by an interaction between the predetermined fourth and fifth voltages. The first driver may apply a predetermined sixth voltage to the maintaining electrodes, while the second driver may apply a predetermined seventh voltage to the maintaining electrodes, in order that a discharge will be caused between those of the scanning and maintaining electrodes where the wall charges have been generated, by an interaction between the predetermined sixth and seventh voltages.
According to the third aspect of the present invention, there is provided a plasma display drive method comprising:
preparing a plasma display panel which includes
a first substrate on which are sequentially formed a matrix of surface discharge electrodes arranged in rows and columns, a plurality of scanning trace electrodes, a plurality of maintaining trace electrodes and a first dielectric layer, each of the surface discharge electrodes comprising a scanning electrode and a maintaining electrode arranged with a predetermined gap in between and which cause a discharge upon a voltage application, each of the scanning trace electrodes connecting the scanning electrodes included in one of the rows of the matrix, the maintaining trace electrodes extending in a direction which is substantially perpendicular to the scanning trace electrodes and intersecting the scanning trace electrodes with insulators being provided between the scanning trace and maintaining trace electrodes, each of the maintaining trace electrodes connecting the maintaining electrodes included in one of the columns of the matrix, the first dielectric layer having an insulation property and covering the scanning electrodes and maintaining electrodes of the surface discharge electrodes, the scanning trace electrodes and the maintaining trace electrodes,
a second substrate facing the first substrate and on which are sequentially formed a second dielectric layer having an insulation property and a plurality of phosphor layers which emit predetermined visible light when they are excited by light generated due to the discharge caused between the scanning and maintaining electrodes, and
a discharge gas filled between the first and second substrates and which generates light due to the discharge caused between the scanning and maintaining electrodes;
applying a predetermined voltage to each of the scanning electrodes through the scanning trace electrodes, thereby causing a discharge between the scanning and maintaining electrodes in order to generate wall charges between the scanning and maintaining electrodes;
applying a predetermined voltage to each of the scanning electrodes through the scanning trace electrodes, while applying a predetermined voltage to each of the maintaining electrodes through the maintaining trace electrodes, thereby erasing the wall charges which have been generated between the scanning and maintaining electrodes;
sequentially applying a predetermined voltage to the scanning electrodes through the scanning trace electrodes in order to select the scanning electrodes row by row, while applying a voltage according to display data to the maintaining electrodes through the maintaining trace electrodes in synchronization with the voltage application to the scanning electrodes, thereby causing a discharge between the scanning and maintaining electrodes in order to generate wall charges between the scanning and maintaining electrodes; and
applying a predetermined voltage to each of the scanning electrodes through the scanning trace electrodes, while applying a predetermined voltage to each of the maintaining electrodes through the maintaining trace electrodes, thereby causing a discharge between those of the scanning and maintaining electrodes where the wall charges have been generated.